In U.S. Pat. No. 4,142,209, Hedlund et al. teach a system which records and reads information on a video disk. Television signals are processed on a real time basis and include address codes within the vertical blanking interval in suitable digital format to identify the location of each field of each video picture frame encoded on the disc for subsequent retrieval purposes. Four identical track address codes are provided in the composite video signal that is to be recorded. The system is also applicable to other forms of encoded data such as audio, audio plus video, x-ray, multiplexed frequency modulation (MFM) and pulse code modulation (PCM) signals and digital data. The recording apparatus may be operated in several modes,including a piecemeal mode for recording on a disc that has already been partly recorded. The piecemeal mode is used when the registration between the transducer and the last recorded track on the disc has been disturbed and cannot be readily reestablished, such as when the disc has been removed from its drive. Other aspects of this system are described by Dietrich in U.S. Pat. Nos. 4,308,557 and 4,488,278.
In U.S. Pat. No. 4,544,835, Drexler describes a data card having a strip of reflective direct-read- after-write laser recording material adhered thereto. The strip is laser recordable to produce 25 micron or smaller spots representing data bits which contrast with the surrounding field of the strip. The strip may have a preinscribed formatting pattern for positioning, timing, programming and related functions.
Each of the various industries, that is, financial, medical, insurance, personal and publishing, has formats specific to its particular needs. Further, each industry or user has an optical data card writing and reading machine, called a "card writer/reader", which may be unique to its own needs. For example, each card writer/reader may use its own particular data encoding scheme requiring track indicia for each prerecorded track on the card containing such information as track numbers, synchronization codes, error correction codes, data location indices and the like. Presently, data cards are custom formatted with track indicia for a particular application and for a particular card writer/reader. A card with pre-formatted track indicia for one machine may not work in machines made by other manufacturers or used in other industries.
It would be desirable to produce a generic type card which is usable in a variety of writer/reader devices or in the same writer/reader used in a variety of industries. Such a card has greater usability and efficiency and could be manufactured in much greater quantity, with greater reliability and lower cost than custom formatted cards and would in some ways be analogous to unformatted magnetic discs. One problem with such an approach is that unlike with magnetic disks the reading and writing optics of card writer/readers imposes a limit on the physical extent of the useful data area of a card and this useful area varies with each machine. Also, unlike unformatted magnetic disks, precision prerecorded tracks on the card are necessary for inexpensive precision tracking with an optical servo.
Accordingly, it is an object of the present invention to provide a method for laser recording on data cards pre-formatted with headerless prerecorded servo track guides which still enables the same card to be used in a variety of write/read machines and for a variety of industries.